HEBERLING LAB

Nothing but sticks!
 
This specimen of flowering dogwood (Cornus florida) doesn’t have any flowers...or leaves!  This specimen of dormant twigs was collected by J.F. Lewis in Union county, Pennsylvania on Christmas Eve, 1934.  This specimen is one of many more like in the Carnegie Museum herbarium collected by Lewis of trees and shrubs in Pennsylvania during winter.  The herbarium at California University of Pennsylvania is named after Lewis (John Franklin Lewis herbarium). It is not immediately clear from the specimens themselves why Lewis collected these, but they likely document a study on winter twigs or to aid the identification of trees in winter.
 
Find this leafless specimen and 240 more collected by J.F. Lewis here: https://midatlanticherbaria.org/portal/collections/list.php?db=328&collector=Lewis%3B+J.F.&includecult=1

(Not quite yet) flowering dogwood
 
This specimen of flowering dogwood (Cornus florida) was collected on January 21, 1906 in Fern Hollow,  Frick Park, Pittsburgh by Otto Jennings.  The specimen was collected 13 years before Frick Park became a city park, bequeathed by the well-known industrialist Henry Clay Frick after his death.  Otto Jennings was an influential botanist in western Pennsylvania, serving as curator at the museum for many years.
 
I’ve said it before, but I’ll say it again -  specimens without leaves are cool!  Why did Jennings collect this specimen?
 
Flowering dogwood has distinctively big flower buds through the winter.  The flower is in there, remaining dormant, waiting to blossom in the spring.  Like many other woody species in our area, the leaf and flower buds are pre-formed  by the previous fall.  They remain dormant until they reach their chilling requirement (number  of cold  days), the air temperature  warms,  and/or the days get longer (in plants, this is called “photoperiod”).   Different species have different requirements, with some species being more conservative than others to prevent premature leaf out in the middle of winter.
 
Only about two and half more months until flowering dogwood awakes in western Pennsylvania. In the meantime, you can admire the species in the spring diorama in Botany Hall, or look for their buds outside.

Find this specimen and more here: http://midatlanticherbaria.org/portal/collections/list.php?db=all&catnum=CM073964&othercatnum=1
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Some dogwoods for the dog days of summer
 
Who doesn’t love a good dogwood? Perhaps you are most familiar with flowering dogwood (Cornus florida), with the beautiful showy white flowers in woods and wooded roadsides across Pennsylvania in the spring.  Or perhaps, the commonly planted Japanese dogwood (Cornus kousa) from...you guessed it...East Asia.  But there are many different dogwood species, all in the genus Cornus.  Species in the genus are distributed across much of the temperate world in the Northern Hemisphere.  Rhoads & Block Plants of Pennsylvania list nine species found in the wild in our state.  They are trees or shrubs (with one exception). The veins on their leaves are quite distinctive, as is their bark and flower structures.
 
Why are these shrubs called dogwood?  There are several stories behind the unique common name. One is that the name was derived from the Celtic word “dag”, referring to its use of its nice wood as a dagger like tools or skewers. Another explanation is that the bard was once used as a treatment of mange for dogs.
 
Four dogwood species were collected on June 28 in Pennsylvania: 69,  37,  26, and 23  years ago:
 
Red-osier dogwood, Cornus sericea (aka Cornus stolonifera) June 28, 1950 in Erie County. Beautiful bright red stems.
 
Gray dogwood, Cornus racemosa June 28, 1982 in Blair County.
 
Cornus ammonum June 28, 1993 in Clarion County.
 
Cornus florida June 28, 1996.  White flowers from the spring are long gone.  (Well, the white structures aren’t actually petals, but modified leaves called bracts that surround a cluster of small yellowish flowers).
 
Over 2,600 dogwood (Cornus) specimens in the Carnegie Museum herbarium from across the world are available online, many with high resolution images: http://midatlanticherbaria.org/portal/collections/list.php?db=328&taxa=cornus&usethes=1&taxontype=2